Vertically accumulating container storage and retrieval systems are know in the art. Exemplary systems are shown in Stingel et al., U.S. Pat. No. 6,729,836; Stingel et al., U.S. Pat. No. 7,200,465; and Stingel et al., U.S. Pat. No. 7,184,855; and Grace, U.S. Pat. No. 4,621,745. The disclosures of the patents are incorporated by reference. In such systems, a first plurality of substantially vertically spaced shelf assemblies is supported by support structure and a second plurality of substantially vertically spaced shelf assemblies is supported by support structure. Each shelf assembly includes a shelf tray for receiving, storing, and discharging containers. The shelf trays of the first plurality of shelf assemblies are substantially staggered vertically relative to the shelf trays of the second plurality of shelf assemblies, with the free ends of the trays of one plurality of shelf assemblies facing the free ends of the trays of the other plurality of shelf assemblies. Each shelf tray is mounted to its respective vertical support for pivotal movement at least between an upwardly tilted receiving position and a downwardly tilted discharge position. A transfer control is operatively connected to the shelf assembly and has a lock position retaining the shelf tray when a shelf tray of a next lower shelf assembly is not prepared to receive a container, and a release position, allowing the shelf to move to the discharge position under the weight of a container disposed on the shelf tray when the shelf tray of the next lower shelf assembly is prepared to receive a container. Containers move downward through the vertical stacks of shelf assemblies from side-to-side in a substantially downward back and forth fashion until a container has reached the lowest open container position.
Biasing is provided to urge the shelf trays to the upwardly tilted receiving position. The biasing has been accomplished by gas cylinders. Gas cylinders are susceptible to degradation due to loss of gas, as well as performance issues which are relative to the temperature of the gas. In a cold environment or during winter months, the performance of the gas cylinders can be markedly different from the performance of the cylinders during warmer months. Changes in gas cylinder performance affects the movement of containers through the towers and can result in unnecessary vibration or jarring of the containers. Replacement, repair, or adjustment of gas cylinders can be time consuming and expensive.